CN113906662A

CN113906662A - Insulation type DCDC converter

Info

Publication number: CN113906662A
Application number: CN202080039935.4A
Authority: CN
Inventors: 河村息吹; 植村匠
Original assignee: Sumitomo Wiring Systems Ltd; AutoNetworks Technologies Ltd; Sumitomo Electric Industries Ltd
Current assignee: Sumitomo Wiring Systems Ltd; AutoNetworks Technologies Ltd; Sumitomo Electric Industries Ltd
Priority date: 2019-06-18
Filing date: 2020-06-03
Publication date: 2022-01-07
Also published as: WO2020255720A1; JP7409169B2; US20220360180A1; US11901825B2; JP2021002991A

Abstract

An insulated DCDC converter (100) is provided with a transformer (10), a full-bridge switching circuit (20), a protection circuit (21), a control unit (40), an inductor (13), and an output circuit (30). The insulated DCDC converter (100) is provided with a first voltage detection unit (40A) for detecting the voltage value between the first conductor path (1) and the second conductor path (2), and a first current detection unit (40C) for detecting the current value of the inductor (13). The control unit (40) determines at least one of the first dead time and the second dead time such that the dead time is increased as the voltage value is increased and the dead time is decreased as the current value is increased, based on the voltage value detected by the first voltage detection unit (40A) and the current value detected by the first current detection unit (40C).

Description

Insulation type DCDC converter

Technical Field

The present disclosure relates to an insulation type DCDC converter.

Background

The insulated DCDC converter is intended to be adapted to a wide input voltage and output load range and maintain high efficiency. As a method for achieving high efficiency, a method (soft switching) is known in which a full-bridge circuit is provided on the primary side of a transformer and a rectifier circuit is provided on the secondary side, and the drain-source voltage of a switching element is reduced to 0V during the dead time of the full-bridge circuit, and then the next switching element is turned on.

Documents of the prior art

Patent document

Patent document 1 Japanese patent laid-open No. 2004-140913

Patent document 2 Japanese patent laid-open publication No. 2016-

Patent document 3 Japanese patent laid-open No. 2013-132112

Disclosure of Invention

Problems to be solved by the invention

Since the time when the voltage between the terminals of the switching element becomes the lowest can be changed by the current flowing through the resonance inductor, it is preferable to change the dead time according to the current of the inductor. However, in each cited document, it is not realized to dynamically obtain the dead time in accordance with the current flowing in the resonance inductor.

The present disclosure provides an insulated DCDC converter which more simply realizes high efficiency.

Means for solving the problems

An insulation type DCDC converter according to one aspect of the present disclosure is a phase shift type insulation type DCDC converter, including: a transformer having a primary coil and a secondary coil; a full-bridge switching circuit including a first switching element, a second switching element, a third switching element, and a fourth switching element; a protection circuit having a first diode and a second diode; a control unit that controls an operation of the switching circuit; an inductor; and an output circuit connected to the secondary side coil, the first switching element and the second switching element being connected in series between a first conductive path and a second conductive path, the third switching element and the fourth switching element being connected in series between the first conductive path and the second conductive path, one end of the inductor being electrically connected to a first connection point between the first switching element and the second switching element, the other end of the inductor being electrically connected to one end of the primary side coil, an anode of the first diode, and a cathode of the second diode, the other end of the primary side coil being electrically connected to a second connection point between the third switching element and the fourth switching element, the cathode of the first diode being electrically connected to the first conductive path, and the anode of the second diode being electrically connected to the second conductive path, the insulated DCDC converter includes: a voltage detection unit that detects a voltage value between the first conductor path and the second conductor path; and a current detection unit that detects a current value of the inductor, wherein the control unit determines at least one of a first dead time and a second dead time based on the voltage value detected by the voltage detection unit and the current value detected by the current detection unit, the first dead time being a time during which both the first switching element and the second switching element are off, and the second dead time being a time during which both the third switching element and the fourth switching element are off, such that the dead time is larger as the voltage value is larger, and the dead time is smaller as the current value is larger.

Effects of the invention

According to the present disclosure, a simple and high-efficiency insulated DCDC converter can be realized.

Drawings

Fig. 1 is a circuit diagram showing an insulated DCDC converter according to embodiment 1.

Fig. 2 is a circuit diagram showing paths of currents flowing through the primary side and the secondary side of the transformer when the first switching element and the fourth switching element are in an on state in the basic insulation type DCDC converter.

Fig. 3 is a circuit diagram showing paths of currents flowing through the secondary side of the transformer when the first switching element, the second switching element, the third switching element, and the fourth switching element are in an off state in the basic insulation type DCDC converter.

Fig. 4 is a circuit diagram showing paths of currents flowing through the primary side and the secondary side of the transformer when the second switching element and the third switching element are in an on state in the basic insulation type DCDC converter.

Fig. 5 is a timing chart showing the timing at which each of the first switching element, the second switching element, the third switching element, and the fourth switching element is switched on and off in the insulated DCDC converter according to embodiment 1.

Fig. 6 shows an enlarged view of the timing chart of the first switching element and the second switching element at time T2 in fig. 5 on the upper side, and a graph showing a change in voltage applied between the drain and the source of the second switching element at time T2 on the lower side.

Fig. 7 is a diagram showing a relationship between a current IL flowing through the inductor and a current Iout flowing through the choke coil.

Fig. 8 is a circuit diagram showing an insulated DCDC converter according to embodiment 2.

Detailed Description

[ description of embodiments of the present disclosure ]

First, embodiments of the present disclosure will be described.

An insulated DCDC converter according to the present disclosure includes a transformer, a full-bridge switching circuit, a protection circuit, a control unit, an inductor, and an output circuit. The transformer has a primary coil and a secondary coil. The full-bridge switching circuit includes a first switching element, a second switching element, a third switching element, and a fourth switching element. The protection circuit has a first diode and a second diode. The control unit controls the operation of the switching circuit. The output circuit is connected to the secondary side coil. The first switching element and the second switching element are connected in series between the first conducting path and the second conducting path. The third switching element and the fourth switching element are connected in series between the first conductive path and the second conductive path. One end of the inductor is electrically connected to a first connection point between the first switching element and the second switching element. The other end of the inductor is electrically connected to one end of the primary side coil, the anode of the first diode, and the cathode of the second diode. The other end of the primary coil is electrically connected to a second connection point between the third switching element and the fourth switching element. The cathode of the first diode is electrically connected to the first conductive circuit. The insulated DCDC converter of the present disclosure is a phase-shift insulated DCDC converter in which the anode of the second diode is electrically connected to the second conductive path. The insulated DCDC converter of the present disclosure includes a voltage detection unit that detects a voltage value between the first conductor path and the second conductor path, and a current detection unit that detects a current value of the inductor. The control unit determines at least one of the first dead time and the second dead time such that the dead time is increased as the voltage value is increased and the dead time is decreased as the current value is increased, based on the voltage value detected by the voltage detection unit and the current value detected by the current detection unit.

In the insulated DCDC converter according to [ 1], the first dead time is a time during which both the first switching element and the second switching element are off. The second dead time is a time when both the third switching element and the fourth switching element are turned off. Therefore, the insulation type DCDC converter can absorb a recovery surge generated in the secondary side coil of the transformer by the protection circuit. At the same time, the insulated DCDC converter calculates a first dead time and a second dead time based on the current value of the current flowing through the inductor detected by the current detection unit. Therefore, the insulation type DCDC converter can dynamically obtain the dead time based on the value corresponding to the current flowing in the inductor.

In the insulated DCDC converter of the above [ 1], the control unit determines whether or not to reflect the excitation inductance of the transformer when determining at least one of the first dead time and the second dead time, based on the increase state of the current value.

The insulated DCDC converter of [ 2] can regard the state of the increase in the current value as the state of the load current. Therefore, the dead time can be obtained more precisely by determining whether or not the excitation inductance is reflected according to the state of the load current, and calculating the first dead time and the second dead time.

In the insulated DCDC converter according to the above [ 2], the control unit may determine at least one of the first dead time and the second dead time by reflecting the excitation inductance when the increase rate of the current value is equal to or less than the threshold value. The control unit may determine at least one of the first dead time and the second dead time without reflecting the excitation inductance when the increase rate of the current value exceeds the threshold value.

In the insulated DCDC converter of [ 3], when the excitation inductance is reflected when the increase rate of the current value is equal to or less than the threshold value, the dead time in a state where the load current is small and the magnitude of the excitation current flowing through the primary coil cannot be ignored is determined. On the other hand, when the increase rate of the current value exceeds the threshold value, the dead time in a state where the load current is large and the magnitude of the excitation current flowing through the primary coil can be ignored is obtained. Therefore, it is possible to obtain a more accurate dead time by reflecting the state of the excitation current flowing in the primary coil according to the magnitude of the load current.

In the insulated DCDC converter according to any one of the above [ 1] to [ 3], the voltage detection unit includes a secondary-side voltage measurement unit that measures a secondary-side voltage applied from a secondary-side coil of the transformer, and detects a voltage value between the first conductive path and the second conductive path based on the secondary-side voltage measured by the secondary-side voltage measurement unit.

The insulated DCDC converter according to the above [ 4] can detect the voltage value between the first conductor path and the second conductor path based on the secondary-side voltage measured by the secondary-side voltage measuring unit. Therefore, the insulated DCDC converter is advantageous in a case where it is difficult to directly measure the voltage value between the first conducting path and the second conducting path or a case where it is more preferable to measure the secondary-side voltage than to directly measure the voltage value and estimate the voltage value.

In the insulated DCDC converter according to the above [ 4], the voltage detector obtains a voltage value between the first conductive path and the second conductive path based on the secondary-side voltage and the turn ratio of the primary coil and the secondary coil.

The insulated DCDC converter according to [ 5 ] above can more easily realize a configuration capable of more accurately obtaining the voltage value between the first conductor path and the second conductor path based on the secondary-side voltage.

The insulated DCDC converter according to any one of [ 4] and [ 5 ], wherein the insulated DCDC converter is a step-down DCDC converter that steps down an input voltage applied between the first conducting path and the second conducting path and outputs an output voltage.

The insulated DCDC converter according to the above [ 6 ] can measure an output voltage which is a value relatively lower than a voltage value between the first conductor path and the second conductor path, and derive a voltage value between the first conductor path and the second conductor path from the output voltage. Therefore, the insulated DCDC converter can omit or simplify a configuration necessary for detecting a high voltage, and can further reduce the size of a configuration capable of detecting a voltage value between the first conducting path and the second conducting path.

The insulated DCDC converter according to any one of [ 4] to [ 6 ] above, wherein the first conductor path and the second conductor path are insulated from the output circuit and the control unit, and the fourth conductor path of a pair of third conductor paths and fourth conductor paths to which an output voltage is applied in the output circuit is electrically connected to a reference conductor path of the control unit.

[ details of embodiments of the present disclosure ]

< embodiment 1 >

[ brief description of the insulated DCDC converter ]

The insulated DCDC converter 100 according to embodiment 1 (hereinafter, also simply referred to as the converter 100) is used as a power supply for outputting electric power for driving an electric drive device (such as a motor) in a vehicle such as a hybrid vehicle or an electric vehicle (ev). The converter 100 transforms an input voltage Vin supplied between the first and second conductive paths 1 and 2 to generate an output voltage Vout, which is applied between the third and fourth conductive paths 3 and 4. As shown in fig. 1, converter 100 includes a transformer 10, a switching circuit 20 provided between first conductor path 1 and transformer 10, an output circuit 30 connected between transformer 10 and third conductor path 3, and a control unit 40 for controlling the operation of switching circuit 20. In actual use, a dc power supply (not shown) is connected between first conductor path 1 and second conductor path 2, and a load 6 is connected between third conductor path 3 and fourth conductor path 4. An input capacitor 7 for stabilizing the input voltage Vin is connected between the first conductor path 1 and the second conductor path 2.

The transformer 10 includes a primary coil 11 and secondary coils 12A and 12B. The number of turns of the primary side coil 11 is N1. The number of turns of each of the secondary side coils 12A and 12B is N2. The secondary side coils 12A, 12B are electrically connected in series with each other at a third connection point P3. The turns ratio N of the transformer 10 is represented as N2/N1. In the transformer 10, a field inductance 14 is formed in parallel with the primary coil 11.

The switching circuit 20 converts an input voltage Vin, which is a dc voltage supplied to the first and second conductive paths 1 and 2, into an ac voltage, and supplies the ac voltage to the primary winding 11 of the transformer 10. The switch circuit 20 has a structure in which a first switch element 20A, a second switch element 20B, a third switch element 20C, and a fourth switch element 20D (hereinafter, also referred to as

switch elements

20A, 20B, 20C, and 20D) are connected in full bridge.

The switching circuit 20 has switching

elements

20A, 20B, 20C, 20D, a first diode 20E, a second diode 20F, and an inductor 13. As the

switching elements

20A, 20B, 20C, and 20D, various known switching elements can be used, but a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) is preferably used.

The

switching elements

20A, 20B, 20C, and 20D are provided with

parasitic diodes

20G, 20H, 20J, and 20K as parasitic components, respectively. Specifically, in each of the

switching elements

20A, 20B, 20C, and 20D, the cathode of each of the

parasitic diodes

20G, 20H, 20J, and 20K is electrically connected to the drain side, and the anode thereof is electrically connected to the source side. In addition to the

parasitic diodes

20G, 20H, 20J, and 20K, diodes may be added as another element.

The

switching elements

20A, 20B, 20C, and 20D are electrically connected in parallel with

capacitors

20L, 20M, 20N, and 20P as capacitance components, respectively. Specifically, one terminal of each of the

capacitors

20L, 20M, 20N, and 20P is electrically connected to the drain of each of the

switching elements

20A, 20B, 20C, and 20D, and the other terminal of each of the

capacitors

20L, 20M, 20N, and 20P is electrically connected to the source. When MOSFETs are used as the

switching elements

20A, 20B, 20C, and 20D, parasitic capacitance components are formed in the

respective switching elements

20A, 20B, 20C, and 20D so that the capacitance components are parasitic. Therefore, the parasitic capacitance component may be used without providing the

capacitors

20L, 20M, 20N, and 20P.

The first switching element 20A and the second switching element 20B are connected in series between the first conductor path 1 and the second conductor path 2 to which the input voltage is input to the switching circuit 20, and are electrically connected to each other at a first connection point P1. The third switching element 20C and the fourth switching element 20D are connected in series between the first conductor path 1 and the second conductor path 2, and are electrically connected to each other at a second connection point P2.

The cathode of the first diode 20E is electrically connected to the first conductor 1 (conductor on the high potential side), and the anode terminal of the second diode 20F is electrically connected to the second conductor 2 (conductor on the low potential side). The anode terminal of the first diode 20E is electrically connected to the cathode terminal of the second diode 20F. The first diode 20E and the second diode 20F constitute a protection circuit 21 that absorbs surge voltages generated in the fifth switching element 30A and the sixth switching element 30B on the secondary side of the transformer 10 through the inductor 13.

One end of the inductor 13 is electrically connected to the first connection point P1. The other end of the inductor 13 is electrically connected to an anode terminal of the first diode 20E, a cathode terminal of the second diode 20F, and one end of the primary coil 11 of the transformer 10. The second connection point P2 is electrically connected to the other end of the primary coil 11. The inductor 13 is provided for the purpose of LC resonance with the

capacitors

20L, 20M, 20N, and 20P in order to reduce switching loss generated in the switching circuit 20. The inductance value of the inductor 13 is preferably set to a value sufficiently larger than the leakage inductance (not shown) of the transformer 10.

The output circuit 30 rectifies and smoothes the ac voltage appearing at the secondary side coils 12A, 12B of the transformer 10 to generate an output voltage Vout which is a dc voltage, and applies the output voltage Vout between the third conductor path 3 and the fourth conductor path 4. The output circuit 30 includes a fifth switching element 30A, a sixth switching element 30B, a rectified output path 30C, a choke coil 33, and an output capacitor 34. The fifth switching element 30A is connected between one end of the secondary winding 12A of the transformer 10 and the ground path G. The sixth switching element 30B is connected between one end of the secondary side coil 12B of the transformer 10 and the ground path G. One end of the rectified output path 30C is electrically connected to a third connection point P3 to which the other end of the secondary-side coil 12A and the other end of the secondary-side coil 12B are electrically connected. One end of the choke coil 33 is electrically connected to the other end of the rectified output path 30C. The other end (i.e., the end on the side away from the third connection point P3) of the choke coil 33 is electrically connected to the third conductor path 3 and to the fourth conductor path 4 via the output capacitor 34. That is, the choke coil 33 is interposed between the third connection point P3 and the third conductive path 3. Output capacitor 34 is electrically connected between third conductive path 3 and fourth conductive path 4. The fourth conductive path 4 is electrically connected to the ground path G.

As the fifth switching element 30A and the sixth switching element 30B, various known switching elements can be used, but MOSFETs are preferably used. The drain of the fifth switching element 30A is electrically connected to one end of the secondary winding 12A, and the source is electrically connected to the ground path G. The sixth switching element 30B has a drain electrically connected to one end of the secondary winding 12B and a source electrically connected to the ground path G. The fifth switching element 30A and the sixth switching element 30B are each provided with a parasitic diode as a parasitic component. Specifically, in each of the fifth switching element 30A and the sixth switching element 30B, a cathode of a parasitic diode is electrically connected to a drain side, and an anode thereof is electrically connected to a source side.

In the output circuit 30 having such a configuration, the fifth switching element 30A and the sixth switching element 30B constitute a rectifier circuit that rectifies the ac voltage appearing at the secondary side coils 12A, 12B of the transformer 10. The choke coil 33 and the output capacitor 34 smooth the rectified output appearing in the rectified output path 30C.

The control Unit 40 is mainly composed of a microcomputer, and includes an arithmetic device such as a CPU (Central Processing Unit), a Memory such as a ROM (Read Only Memory) or a RAM (Random Access Memory), an a/D converter, and the like. The control unit 40 is configured to recognize the voltage value of the first conductive path 1 by the first voltage detection unit 40A. The control unit 40 is configured to recognize the voltage value of the third conductive path 3 by the second voltage detection unit 40B. The first voltage detection unit 40A and the second voltage detection unit 40B are configured as a known voltage detection circuit. The control unit 40 is configured to recognize the value of the current flowing through the first conductive path 1 by the first current detection unit 40C. The controller 40 is configured to recognize the value of the current flowing through the third conductive path 3 by the second current detector 40D. The first current detection unit 40C and the second current detection unit 40D are configured as a known current detection circuit such as a current transformer.

Based on the values input from first voltage detector 40A, second voltage detector 40B, first current detector 40C, and second current detector 40D, controller 40 outputs PWM signals to the gates of switching

elements

20A, 20B, 20C, and 20D by a phase shift method. Thus, the

switching elements

20A, 20B, 20C, and 20D perform a switching operation by the phase shift method. The control unit 40 may be configured to output a switching signal at a predetermined timing to the gates of the fifth switching element 30A and the sixth switching element 30B based on values input from the first voltage detection unit 40A, the second voltage detection unit 40B, the first current detection unit 40C, and the second current detection unit 40D, and the like.

[ operation of insulated DCDC converter ]

Next, the operation of the converter 100 will be described. In a vehicle equipped with the converter 100, for example, an ignition switch is switched from an off state to an on state. In this way, the control unit 40 outputs the PWM signals to the

switching elements

20A, 20B, 20C, and 20D, and outputs the switching signals at predetermined timings to the fifth switching element 30A and the sixth switching element 30B, respectively.

Basically, as shown in fig. 2 to 4, in the insulated DCDC converter having the switching circuits connected in the full bridge, the first switching element 120A and the fourth switching element 120D of the switching circuit 120 are alternately turned on and off repeatedly, and the second switching element 120B and the third switching element 120C are alternately turned on and off. This allows the output circuit 130 to generate an output voltage by operating to apply an alternating-current voltage from the direct-current power supply to the primary coil 111 of the transformer 110. Specifically, when the first switching element 120A and the fourth switching element 120D are turned on, a current flows through a path indicated by an arrow C1 on the switching circuit 120 side (the primary side of the transformer 110). The path indicated by the arrow C1 is the path of the first conductive path 101 → the first switching element 120A → the primary-side coil 111 → the fourth switching element 120D → the second conductive path 102. Accordingly, a current flows through a path indicated by an arrow C2 on the output circuit 130 side (secondary side of the transformer 110). The path indicated by the arrow C2 is a path of the fourth conductive path 104 → the sixth switching element 130B → the secondary side coil 112B → the rectified output path 130C → the choke coil 133 → the third conductive path 103 (refer to fig. 2.).

Next, the first switching element 120A and the fourth switching element 120D are switched from on to off, and the first switching element 120A, the second switching element 120B, the third switching element 120C, and the fourth switching element 120D are all turned off. Thus, no current flows to the switching circuit 120 (primary side of the transformer 110). On the output circuit 130 side (secondary side of the transformer 110), a current flows through a path indicated by an arrow C3 or an arrow C4 by the energy stored in the choke coil 133. The path indicated by the arrow C3 is a path of the fourth conductive path 104 → the sixth switching element 130B → the secondary side coil 112B → the rectified output path 130C → the choke coil 133 → the third conductive path 103. The path indicated by the arrow C4 is a path of the fourth conductive path 104 → the fifth switching element 130A → the secondary-side coil 112A → the rectified output path 130C → the choke coil 133 → the third conductive path 103 (refer to fig. 3.).

Next, the second switching element 120B and the third switching element 120C are switched from off to on. Thus, a current flows through a path indicated by an arrow C5 on the side of the switching circuit 120 (the primary side of the transformer 110). The path indicated by the arrow C5 is a path of the first conductive path 101 → the third switching element 120C → the primary side coil 111 → the second switching element 120B → the second conductive path 102. In response to this, a current flows through a path indicated by an arrow C6 on the output circuit 130 side (secondary side of the transformer 110). The path indicated by the arrow C6 is a path of the fourth conductive path 104 → the fifth switching element 130A → the secondary-side coil 112A → the rectified output path 130C → the choke coil 133 → the third conductive path 103 (refer to fig. 4.).

Next, the second switching element 120B and the third switching element 120C are switched from on to off, and the first switching element 120A, the second switching element 120B, the third switching element 120C, and the fourth switching element 120D are all turned off. Thus, no current flows to the switching circuit 120 (primary side of the transformer 110). On the output circuit 130 side (secondary side of the transformer 110), a current flows through a path indicated by an arrow C3 or an arrow C4 by the energy stored in the choke coil 133. The path indicated by the arrow C3 is a path of the fourth conductive path 104 → the sixth switching element 130B → the secondary side coil 112B → the rectified output path 130C → the choke coil 133 → the third conductive path 103. The path indicated by the arrow C4 is a path of the fourth conductive path 104 → the fifth switching element 130A → the secondary-side coil 112A → the rectified output path 130C → the choke coil 133 → the third conductive path 103 (refer to fig. 3.).

In contrast, the converter 100 of the present disclosure performs a switching operation by a phase shift method. As shown in fig. 5, the phase shift manner is a manner controlled as follows: the timing of the on/off operation of each of the first switching element 20A and the fourth switching element 20D is shifted, the timing of the on/off operation of each of the second switching element 20B and the third switching element 20C is shifted, and the timing of the on/off operation of each of the

switching elements

20A, 20B, 20C, and 20D is shifted. This realizes ZVS (Zero Voltage Switching) when the

Switching elements

20A, 20B, 20C, and 20D are switched from off to on, and enables the converter 100 to operate more efficiently. In the phase shift method, the first switching element 20A and the second switching element 20B are handled as one set (hereinafter, also referred to as a first branch), and the third switching element 20C and the fourth switching element 20D are handled as one set (hereinafter, also referred to as a second branch). In the first branch, the time (T2, T4, T6, T8 in fig. 5) at which the first switching element 20A and the second switching element 20B are both off is the first dead time. In the second branch, the time (T1, T3, T5, T7 in fig. 5) when the third switching element 20C and the fourth switching element 20D are both off is the second dead time.

Here, a case where the second switching element 20B is switched from off to on in the first dead time will be described with attention being paid to the time T2. As shown in fig. 6, before time T2S (i.e., when the first switching element 20A is turned on), the input voltage Vin of direct current is applied between the drain and the source of the second switching element 20B (see the lower side of fig. 6). At this time, the input voltage Vin of the direct current is also applied to the capacitor 20M connected in parallel with the second switching element 20B. Then, when the first switching element 20A is switched from on to off at time T2S, no current flows through the first switching element 20A. At this time, LC resonance starts between the capacitor 20M connected in parallel to the second switching element 20B and the inductor 13, and the voltage between the drain and the source of the second switching element 20B is close to half the magnitude of the input voltage Vin of direct current. The voltage between the drain and the source of the second switching element 20B is closest to 0V at time T2E when the voltage first decreases after the start of LC resonance (refer to the lower side of fig. 6). Therefore, ZVS of the second switching element 20B can be realized by setting the time at which the second switching element 20B is switched from off to on to T2E. Further, the second switching element 20B may be switched from off to on to a time slightly earlier than T2E.

Although the description has been given with a view to the case where the second switching element 20B is switched from off to on in the first dead time at the time T2, the same applies to the case where the other times T1, T3, T4, T5, T6, T7, T8 and the

other switching elements

20A, 20C, 20D are switched from off to on in fig. 5.

Here, the first dead time (tdead _ a) in the first branch can be obtained by a mathematical expression shown by the numeral 1.

[ number 1]

In addition, the second dead time (tdead _ b) in the second branch can be obtained by the numerical expression shown by the number 2.

[ number 2]

Here, Vin is an input voltage of the dc power supply. N is a turn ratio between the number of turns N1 of the primary side coil 11 and the number of turns N2 of the secondary side coil 12A or 12B. Vout is the voltage applied between the third conductor path 3 and the fourth conductor path 4. IL is the current flowing in the inductor 13. Ca1 is the electrostatic capacitance of capacitor 20L. Ca2 is the electrostatic capacitance of capacitor 20M. Cb1 is the electrostatic capacitance of capacitor 20N. Cb2 is the electrostatic capacitance of the capacitor 20P. L is the inductance of the inductor 13. Lchoke is the inductance of the choke coil 33.

The right side of each of tdead _ a and tdead _ b of the expressions shown by the numbers 1 and 2 is the time from the time when one switching element is switched off and both switching elements are off in the first branch and the second branch to the time when the voltage between the drain and the source of the other switching element is first minimized by LC resonance. That is, the time is set to a first dead time (tdead _ a) and a second dead time (tdead _ b).

The control unit 40 detects Vin by the first voltage detection unit 40A and detects Vout by the second voltage detection unit 40B. IL is detected by the first current detection unit 40C. In this way, the control unit 40 can obtain Vin, IL, and Vout, and dynamically calculate the first dead time (tdead _ a) and the second dead time (tdead _ b) by calculating them based on the mathematical expressions shown by the numbers 1 and 2. Then, the PWM signals are output to the

switching elements

20A, 20B, 20C, and 20D so as to obtain the calculated first dead time (tdead _ a) and second dead time (tdead _ B). This enables ZVS to be realized in the

switching elements

20A, 20B, 20C, and 20D.

According to the equations shown in the equation 1 and the equation shown in the equation 2, the dead time increases as the value of the input voltage Vin of the dc power supply (i.e., the voltage value detected by the first voltage detection unit 40A) increases, and the dead time decreases as the value of the current IL flowing through the inductor 13 (i.e., the current value detected by the first current detection unit 40C) increases. In addition, the dead time increases as the value of the output voltage Vout applied between the third conductor path 3 and the fourth conductor path 4 (i.e., the voltage value detected by the second voltage detection unit 40B) increases.

Next, a case where the current in the choke coil 33 is in the discontinuous mode will be described. A relationship such as a graph shown in fig. 7 exists between the current IL flowing in the inductor 13 and the current Iout flowing in the load 6 (i.e., the current flowing in the choke coil 33). In fig. 7, when Iout is larger than Ic, the current in the choke coil 33 is in the continuous mode, and when Iout is equal to or smaller than Ic, the current in the choke coil 33 is in the negative continuous mode. When the magnitude of the current of Iout is larger than Ic (that is, in the case of the continuous mode), the relationship between Iout and IL is proportional to IL, i.e., Iout/N. N is a turn ratio between the number of turns N1 of the primary side coil 11 and the number of turns N2 of the secondary side coil 12A or 12B. In the case of the continuous mode, the first dead time (tdead _ a) and the second dead time (tdead _ b) are dynamically calculated based on the mathematical expressions shown by the numbers 1 and 2.

In contrast, when the excitation current flows from the secondary side coils 12A and 12B along the primary side coil 11, the dead time may be calculated using an arithmetic expression different from the mathematical expression of the number 1 or the number 2. The excitation current has a property of flowing through the secondary side coils 12A, 12B when the load current is relatively large and flowing through the primary side coil 11 when the load current is relatively small. Therefore, when the magnitude of Iout is Ic or less, a proportional relationship is established in which the slope is smaller than that of a straight line having IL (Iout/N) (that is, a slope smaller than 1/N). This reflects the property that the excitation current flowing through the primary-side coil 11 increases when the size of Iout is Ic or less, and the excitation current flowing through the primary-side coil 11 becomes larger as Iout approaches 0. Therefore, the rate of increase (i.e., slope) of the current in the interval where Iout is 0 to Ic is smaller than the rate of increase (i.e., slope) in the interval larger than Ic. The increase rate in the interval of Iout from 0 to Ic is reflected in the current IL flowing in the inductor 13, and therefore is smaller than the increase rate (i.e., slope 1/N) in the interval greater than Ic. For example, the following methods are considered: the control unit 40 monitors the increase rate of Iout or IL, and compares a predetermined threshold value stored in the control unit 40 in advance with the increase rate to detect Ic.

Here, when the excitation current flows through the primary coil 11 (i.e., the interval of Iout from 0 to Ic in fig. 7), the first dead time (tdead _ a) in the first branch can be obtained by the mathematical expression shown by the numeral 3.

[ number 3]

In addition, when the current flowing through the choke coil 33 is in the discontinuous mode, the second dead time (tdead _ b) in the second branch can be obtained by a mathematical expression shown by the numeral 4.

[ number 4]

Here, Lmag is the value of the magnetizing inductance 14. The right side of each of tdead _ a and tdead _ b of the expressions shown by the numbers 3 and 4 is the time from the time when one switching element is switched off and both switching elements are off in the first branch and the second branch to the time when the voltage between the drain and the source of the other switching element is first minimized by LC resonance. That is, the time is set to the first dead time (tdead _ a) and the second dead time (tdead _ b) in the discontinuous mode.

Therefore, when the current flowing through the choke coil 33 is in the discontinuous mode (i.e., when Ic or less), the control unit 40 can calculate and dynamically calculate the first dead time (tdead _ a) and the second dead time (tdead _ b) by reflecting the value of the excitation inductance 14 based on the mathematical expressions shown by the numbers 3 and 4. Then, the PWM signals are output to the

switching elements

20A, 20B, 20C, and 20D so as to obtain the calculated first dead time (tdead _ a) and second dead time (tdead _ B). Thus, ZVS can be realized in the

switching elements

20A, 20B, 20C, and 20D even when the excitation current flows through the primary coil 11. That is, the control unit 40 determines whether or not the excitation inductance 14 of the transformer 10 is reflected in determining the first dead time and the second dead time, based on the increase state of the current Iout flowing through the choke coil 33 (i.e., the current IL flowing through the inductor 13).

According to the equations shown in the equation 3 and the equation shown in the equation 4, the dead time increases as the value of the input voltage Vin of the dc power supply (i.e., the voltage value detected by the first voltage detection unit 40A) increases, and the dead time decreases as the value of the current IL flowing through the inductor 13 (i.e., the current value detected by the first current detection unit 40C) increases. In addition, the dead time increases as the value of the output voltage Vout applied between the third conductor path 3 and the fourth conductor path 4 (i.e., the voltage value detected by the second voltage detection unit 40B) increases.

Next, the effects of the present structure are exemplified.

The insulated DCDC converter 100 according to the present disclosure includes a transformer 10, a full-bridge switching circuit 20, a protection circuit 21, a control unit 40, an inductor 13, and an output circuit 30. The transformer 10 has a primary coil 11 and secondary coils 12A and 12B. The full-bridge switching circuit 20 includes switching

elements

20A, 20B, 20C, and 20D. The protection circuit 21 has a first diode 20E and a second diode 20F. The control unit 40 controls the operation of the switching circuit 20. The output circuit 30 is connected to the secondary side coils 12A and 12B. The first switching element 20A and the second switching element 20B are connected in series between the first conductor path 1 and the second conductor path 2. Third switching element 20C and fourth switching element 20D are connected in series between first conductor path 1 and second conductor path 2. One end of the inductor 13 is electrically connected to a first connection point P1 between the first switching element 20A and the second switching element 20B. The other end of the inductor 13 is electrically connected to one end of the primary-side coil 11, the anode of the first diode 20E, and the cathode of the second diode 20F. The other end of the primary coil 11 is electrically connected to a second connection point P2 between the third switching element 20C and the fourth switching element 20D. A cathode of the first diode 20E is electrically connected to the first conductive circuit 1. The insulated DCDC converter 100 of the present disclosure is a phase-shift insulated DCDC converter in which the anode of the second diode 20F is electrically connected to the second conductive path 2. The insulated DCDC converter 100 of the present disclosure includes a first voltage detection unit 40A that detects a voltage value between the first conductor path 1 and the second conductor path 2, and a first current detection unit 40C that detects a current value of the inductor 13. Based on the voltage value detected by first voltage detection unit 40A and the current value detected by first current detection unit 40C, control unit 40 determines at least one of the first dead time and the second dead time such that the dead time is increased as the voltage value is increased and the dead time is decreased as the current value is increased. The first dead time is a time when both the first switching element 20A and the second switching element 20B are turned off. The second dead time is a time when both the third switching element 20C and the fourth switching element 20D are turned off.

Therefore, the insulation type DCDC converter 100 can absorb the recovery surge generated on the secondary side of the transformer 10 by the protection circuit 21. At the same time, the insulated DCDC converter 100 calculates the first dead time and the second dead time based on the current value of the current IL flowing through the inductor 13 detected by the first current detection unit 40C. Therefore, the insulation type DCDC converter 100 can dynamically obtain the dead time based on the value corresponding to the current flowing in the inductor 13.

The control unit 40 of the insulated DCDC converter 100 according to the present disclosure determines whether or not the excitation inductance 14 of the transformer 10 is reflected in determining the first dead time and the second dead time based on the increase state of the current value.

With this configuration, the state of the increase in the current value can be regarded as the state of the load current. Therefore, the dead time can be obtained more precisely by determining whether or not the excitation inductance 14 is reflected according to the state of the load current, and calculating the first dead time and the second dead time.

The control unit 40 of the insulated DCDC converter 100 according to the present disclosure determines at least one of the first dead time and the second dead time by reflecting the excitation inductance 14 when the increase rate of the current value is equal to or less than the threshold value. When the increase rate of the current value exceeds the threshold value, the control unit 40 determines the first dead time and the second dead time without reflecting the excitation inductance 14.

With this configuration, when the exciting inductance 14 is reflected when the increase rate of the current value is equal to or less than the threshold value, the dead time is obtained in a state where the load current is small and the magnitude of the exciting current flowing through the primary winding 11 cannot be ignored. On the other hand, if the field inductance 14 is not reflected when the increase rate of the current value exceeds the threshold value, the dead time is determined in which the load current is large and the magnitude of the field current flowing through the primary coil 11 can be ignored. Therefore, it is possible to obtain a more accurate dead time by reflecting the state of the excitation current flowing in the primary coil according to the magnitude of the load current.

< embodiment 2 >

The following description relates to an insulated DCDC converter 200 according to embodiment 2 shown in fig. 8.

The insulated DCDC converter 200 according to embodiment 2 is different from the insulated DCDC converter 100 according to embodiment 1 in that the first voltage detector 40A is omitted (first difference). Further, the insulated DCDC converter 200 according to embodiment 2 is different from the insulated DCDC converter 100 according to embodiment 1 in that a secondary-side voltage detection unit 40E is provided (second difference). Further, the insulated DCDC converter 200 according to embodiment 2 is different from the insulated DCDC converter 100 according to embodiment 1 in that "the voltage value between the first conductor path 1 and the second conductor path 2" is detected by a method different from that of embodiment 1 (a third difference). On the other hand, the configuration, operation, and the like of the insulated DCDC converter 200 according to embodiment 2 are all the same as those of the insulated DCDC converter 100 according to embodiment 1, except for the first difference, the second difference, and the third difference.

The insulation type DCDC converter 200 according to embodiment 2 is also a step-down type DCDC converter that steps down an input voltage Vin, which is a direct-current voltage applied between the first conductor path 1 and the second conductor path 2, and outputs an output voltage Vout, which is a direct-current voltage lower than the input voltage Vin.

In the insulated DCDC converter 200, the secondary-side voltage detection unit 40E and the control unit 40 correspond to an example of a voltage detection unit.

The secondary-side voltage detection unit 40E measures a secondary-side voltage Vtr2 applied from the secondary-side coils 12A and 12B of the transformer 10. The secondary-side voltage Vtr2 is a potential difference between the rectified output path 30C (fifth conductor path) electrically connected to the transformer 10 and the fourth conductor path 4 electrically connected to the ground. The rectified output path 30C is a conductive path between the choke coil 33 and an intermediate position (center tap) of the secondary side coils 12A and 12B in the transformer 10. That is, the secondary-side voltage Vtr2 is a voltage of the rectified output path 30C (fifth conductor path) with reference to the potential (ground potential) of the fourth conductor path 4. The secondary-side voltage Vtr2 is a value indicating a voltage across the secondary-side coils 12A and 12B, which is a value before being smoothed by a filter circuit including the choke coil 33 and the output capacitor 34. The value indicated by the second voltage detector 40B is the potential difference between the third conductor path 3 and the fourth conductor path 4, and the voltage between both ends is the value of the dc voltage smoothed by the filter circuit. The secondary-side voltage detection unit 40E inputs a signal indicating the value of the secondary-side voltage Vtr2 to the control unit 40. The signal indicating the value of the secondary-side voltage Vtr2 may be a signal indicating the value of the secondary-side voltage Vtr2 itself, or a signal indicating a value obtained by dividing the secondary-side voltage Vtr2 at a predetermined division ratio, as long as the signal can specify the value of the secondary-side voltage Vtr 2.

The control unit 40 detects a voltage value between the first conductor path 1 and the second conductor path 2 based on the secondary-side voltage Vtr2 measured by the secondary-side voltage detection unit 40E. The voltage value between the first and second conductive paths 1, 2 is the value of the input voltage Vin and is the potential difference between the first and second conductive paths 1, 2.

The control unit 40 sets the value of the secondary-side voltage to Vtr2, sets the turn ratio between the primary coil 11 and the secondary-side coil 12A and the turn ratio between the primary coil 11 and the secondary-side coil 12B to N, and sets the voltage value (value of the input voltage) between the first conductor path 1 and the second conductor path 2 to Vin. The number of turns of the primary coil 11 is N1, and the number of turns of the secondary coils 12A and 12B is N2. The turn ratio N is N1/N2. On the premise that Vin is equal to Vtr2 × N, the control unit 40 obtains Vin by an equation. In the insulated DCDC converter 200, control using Vin is the same as in embodiment 1, and control other than Vin is also the same as in embodiment 1.

In this way, the insulated DCDC converter 200 according to embodiment 2 can detect the voltage value (the value of the input voltage Vin) between the first conductor path 1 and the second conductor path 2 based on the secondary-side voltage Vtr2 measured by the secondary-side voltage measuring unit. Therefore, the insulated DCDC converter is advantageous in the case where it is difficult to directly measure the voltage value (the value of the input voltage Vin) between the first conductor path 1 and the second conductor path 2 or in the case where it is more preferable to measure the secondary-side voltage Vtr2 than to directly measure the voltage value and estimate the voltage value.

The insulated DCDC converter 200 can more easily realize a configuration in which the voltage value (the value of the input voltage Vin) between the first conductor path 1 and the second conductor path 2 can be more accurately obtained based on the secondary-side voltage Vtr2 based on the turn ratio N. The above-described calculation method (Vin ═ Vtr2 × N) is merely an example, and any other calculation method may be used as long as the input voltage Vin can be calculated based on the secondary-side voltage Vtr2 and the turn ratio of the transformer.

The insulated DCDC converter 200 is capable of measuring a secondary-side voltage Vtr2, which is a relatively low value compared to a voltage value between the first conductor path 1 and the second conductor path 2 (a value of the input voltage Vin), and deriving a voltage value between the first conductor path 1 and the second conductor path 2 from the secondary-side voltage Vtr 2. Therefore, the insulated DCDC converter 200 can omit or simplify a configuration necessary for detecting a high voltage, and can further reduce the size of a configuration capable of detecting a voltage value between the first conductor path 1 and the second conductor path 2. For example, in the case where the value of the input voltage Vin is directly measured and the measured value is input to the control unit 40, when the value of the input voltage Vin increases, an insulating unit such as an insulating amplifier is necessary between the input side and the control unit 40, but such a component can be omitted according to the method of embodiment 2.

In particular, in the present configuration, the secondary side coils 12A and 12B and the rectification output path 30C are insulated from both the first conductive path 1 and the second conductive path 2, and the fourth conductive path 4 is insulated from both the first conductive path 1 and the second conductive path 2. The fourth conductor path 4 is electrically connected to a reference conductor path, not shown, in the control unit 40, and the fourth conductor path 4 has the same potential as the reference conductor path of the control unit 40. Therefore, the measurement result of the secondary-side voltage Vtr2 can be favorably input to the control unit 40 without being insulated, and the "measurement path of the secondary-side voltage Vtr2 and the control unit 40" and the "first conductor path 1 and the second conductor path 2" on the input side can be reliably insulated from each other.

< other embodiments >

The present configuration is not limited to the embodiments described above and illustrated in the drawings, and for example, the following embodiments are also included in the technical scope of the present invention.

In embodiments 1 and 2, the first dead time (tdead _ a) and the second dead time (tdead _ b) are calculated and calculated by the control unit 40, but the control unit may store a data table in which the first dead time and the second dead time corresponding to the input voltage, the current flowing through the inductor, and the output voltage are stored, and the switching elements may be switched from off to on based on the first dead time and the second dead time corresponding to the input voltage, the current flowing through the inductor, and the output voltage obtained by calculation from the data table.

In embodiments 1 and 2, the fifth switching element 30A and the sixth switching element 30B use MOSFETs, but may be configured to use diodes.

In embodiments 1 and 2, the control unit 40 is mainly configured by a microcomputer, but may be implemented by a plurality of hardware circuits other than the microcomputer.

In embodiments 1 and 2, both the first dead time and the second dead time are obtained, but at least either one of the first dead time and the second dead time may be obtained.

In embodiment 1, the voltage value of the input voltage Vin is detected by the first voltage detector 40A, but the input voltage Vin may be calculated by calculation based on the voltage value of the output voltage Vout detected by the second voltage detector, the turn ratio of the transformer, and the duty ratio of the PWM signal. Alternatively, in the configuration of embodiment 1, the value of the input voltage Vin may be detected as in embodiment 2.

In embodiments 1 and 2, the current IL flowing through the inductor 13 is detected by the first current detecting unit 40C provided in the first conductive path 1, but the position and configuration of the current detecting unit may be any position and configuration as long as it can detect the current flowing through the inductor.

The embodiments disclosed herein are illustrative and not restrictive in all respects. The scope of the present invention is not limited to the embodiments disclosed herein, but is defined by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

Description of the reference numerals

1 … first conductive path

2 … second conductive path

3 … third conductive path

4 … fourth conductive path

6 … load

7 … input capacitor

10 … transformer

11 … primary coil

12A, 12B … secondary side coil

13 … inductor

14 … magnetizing inductance

20 … switching circuit

20A … first switching element

20B … second switching element

20C … third switching element

20D … fourth switching element

20E … first diode

20F … second diode

20G, 20H, 20J, 20K … parasitic diode

20L, 20M, 20N, 20P … capacitor

21 … protection circuit

30 … output circuit

30A … fifth switching element

30B … sixth switching element

30C … rectified output path

33 … choke coil

34 … output capacitor

40 … control part (Voltage detecting part)

40A … first Voltage detection section (Voltage detection section)

40B … second Voltage detection section (Voltage detection section)

40C … first Current detecting section (Current detecting section)

40D … second current detection part

40E … Secondary side Voltage detection section (Voltage detection section)

100. 200 … insulation type DCDC converter

101 … first conductive path

102 … second conductive path

103 … third conductive path

104 … fourth conductive path

110 … transformer

111 … primary coil

112A, 112B … secondary side coil

120 … switching circuit

120A … first switching element

120B … second switching element

120C … third switching element

120D … fourth switching element

130 … output circuit

130a … fifth switching element

130B … sixth switching element

130C … rectified output path

133 … choke coil

G … ground path

P1 … first connection point

P2 … second connection Point

P3 … third connection Point

Vin … input voltage

Vout … output voltage

Vtr2 … secondary side voltage.

Claims

1. An insulation type DCDC converter of a phase shift system includes:

a transformer having a primary coil and a secondary coil;

a full-bridge switching circuit including a first switching element, a second switching element, a third switching element, and a fourth switching element;

a protection circuit having a first diode and a second diode;

a control unit that controls an operation of the switching circuit;

an inductor; and

an output circuit connected to the secondary side coil,

the first switching element and the second switching element are connected in series between a first conductor path and a second conductor path,

the third switching element and the fourth switching element are connected in series between the first conductive path and the second conductive path,

one end of the inductor is electrically connected to a first connection point between the first switching element and the second switching element,

the other end of the inductor is electrically connected with one end of the primary side coil, the anode of the first diode and the cathode of the second diode,

the other end of the primary side coil is electrically connected to a second connection point between the third switching element and the fourth switching element,

a cathode of the first diode is electrically connected to the first conducting circuit,

the anode of the second diode is electrically connected to the second conductive path,

the insulated DCDC converter includes:

a voltage detection unit that detects a voltage value between the first conductor path and the second conductor path; and

a current detection unit for detecting a current value of the inductor,

the control unit determines at least one of a first dead time and a second dead time based on the voltage value detected by the voltage detection unit and the current value detected by the current detection unit, the first dead time being a time during which both the first switching element and the second switching element are turned off, and the second dead time being a time during which both the third switching element and the fourth switching element are turned off, such that the dead time is increased as the voltage value is increased and the dead time is decreased as the current value is increased.

2. The insulated DCDC converter according to claim 1,

the control unit determines whether or not to reflect the excitation inductance of the transformer when determining at least one of the first dead time and the second dead time, based on an increase state of the current value.

3. The insulated DCDC converter according to claim 2,

the control unit determines at least one of the first dead time and the second dead time by reflecting the excitation inductance when the increase rate of the current value is equal to or less than a threshold value, and determines at least one of the first dead time and the second dead time without reflecting the excitation inductance when the increase rate of the current value exceeds the threshold value.

4. The insulated DCDC converter according to any one of claims 1 to 3,

the voltage detection unit includes a secondary-side voltage measurement unit that measures a secondary-side voltage applied from the secondary coil of the transformer, and detects the voltage value based on the secondary-side voltage measured by the secondary-side voltage measurement unit.

5. The insulated DCDC converter according to claim 4,

the voltage detection unit obtains the voltage value based on the secondary side voltage and a turn ratio of the primary side coil and the secondary side coil.

6. The insulation-type DCDC converter according to claim 4 or 5,

the insulation type DCDC converter is a step-down type DCDC converter that steps down an input voltage applied between the first conductive path and the second conductive path and outputs the output voltage.